Ellipse protractors for mechanical drawings



Aug. 11, 1964 F. R. SHARP 3,143,806

ELLIPSEI PROTRACTORS FOR MECHANICAL DRAWINGS Filed Oct. 9, 1962 4 Sheets-Sheet 1 HomzoNTAL STRAIGHT EDGE.) 2

INVENTOR. FLOYD SHARP ATTORNEY Aug. 11, 1964 F. R. SHARP 3,143,806

ELLIPSE PROTRACTORS FOR MECHANICAL DRAWINGS Filed Oct. 9, 1962 4 Sheets-Sheet 2 INVENTOR.

FLOYD SHARP ATTORNEY Aug. 11, 1964 F. R. SHARP 3,143,806

ELLIPSE PROTRACTORS FOR MECHANICAL DRAWINGS Filed Oct. 9, 1962 4 Sheets-Sheet 3 INVENTOR. FLOYD SHARP ATTORNEY Aug. 11, 1964 F. R. SHARP ELLIPSE. PROTRACTORS FOR MECHANICAL DRAWINGS 4 SheetS=-Sheet 4.

Filed 001:. 9,

36-60 TFUANGLE HOB EONTAL STRAIGH m m M FLOYD SHARP JTTOBA/EY United States Patent 3,143,806 ELLESE fiiGTRACTORS FOR MECHANICAL DRAWINGS Floyd R. Sharp, 2849 Brunswick Ave., St. Louis Park, Minn. Fiied Get. 9, 1962, Ser. No. 229,309 13 Claims. (til. 33-91) This invention relates to mechanical drawing instruments and particularly concerns ellipse protractors useful in axonometric one plane representations of threedimensional objects.

A primary object is to provide an ellipse protractor with two coupled straight edge arms simultaneously adjustable on a protractor plate for locating and drawing ninety degree perspectively related angles in a plane when that plane may be rotated on its axis.

A further object is to provide a protractor as described for isometric ellipses, including a base upon which the protractor plate is angularly adjustable to any one of three plane positions depending on which one of the three axes of an isometric projection is determined as the axis of rotation.

Still another object is to provide protractors having adjustable arms on protractor plates and with or without adjustable bases for locating and drawing ninety degree related angles when rotated about the pertinent axis, in various dimetric and trimetric systems.

A still further object is to provide instruments as described based on ellipses ranging in five degree steps from about ten degrees to eighty degrees, to facilitate drawing compound as well as simple angular deviations which may occur in any axonometric system selected.

For further comprehension of the invention, and of the objects and advantages thereof, reference will be had to the following description and accompanying drawings, and to the appended claims in which the various novel features of the invention are more particularly set forth.

In the accompanying drawings forming a material part of this disclosure:

FIG. 1 is a plan view of a protractor embodying the invention, together with an isometric drawing of a cube illustrating how the protractor may be used.

FIG. 2 is a rear view of the protractor, the arms of which are in a different position from that shown in FiG. 1.

FIG. 3 is an edgewise elevational view of the protractor.

PEG. 4 is an exploded isometric view of the protractor.

FIG. 5 is an exploded isometric view of parts of the protractor lying within the area bounded by dotted line 5 in FIG. 4.

FIG. 6 is a plan view on an enlarged scale of the pro tractor plate of the protractor shown in FIGS. 14.

FIGS. 7Zand 8 are plan views of other protractor plates according to the invention.

FIG. 9 is a plan view of another protractor embodying the invention.

FIG. 10 is a rear view of part of the protractor of P16. 9.

FIG. 11 is a plan view of the protractor of FIG. 9 with associated straight edge and triangle drawing instruments, md an isometric drawing of a cube, illustrating how the protractor may be used.

FIG. 12 is a plan view of another protractor illustrating another embodiment of the invention.

3,143,895 Patented Aug. 11, 1964 ice FIG. 13 is a diagram used in explaining basic features and principles of the invention.

Referring first to FIGS. 1-6, there is shown the drawing instrument which includes a protractor plate 22. This plate has peripheral numbered graduations 24 ruled in elliptical degrees for the isometric ellipse l6). The plate has an arcuate circularly curved trammel such as slot 26, and has a hole 28 at the geometrical center of the trammel slot 26. A circularly curved slot 30 is located below slot 26. A hole 32 is located at the geometrical center of slot 39 between the ends of slot 26. The graduations G at four 0 locations spaced ninety elliptical degrees apart may be emphasized by placement of enlarged zero indicia 36 at graduations spaced from the slots 26 and 30. Three points or indices 38, 39 and 40 are marked LEFT, RIGHT and HOR., respectively. These points are spaced sixty true degrees apart (ninety elliptical degrees between LEFT and RIGHT, forty-five elliptical degrees between RIGHT and HORJ. They are located below and laterally of slot 30.

The instrument 20 further includes two straight arms 42, 44 which may have pointed ends 46, 48 slanted from outer short edges 43, toward inner longer edges 31, 33. Near the ends of the longer edges opposite from the pointed ends are spacer elements 49*, 49 formed as projections on the upper surfaces of the arms. Holes 50 are formed near the rounded ends of the arms in alignment with the inner edges 31 and 33. The rounded ends of the arms are widened at 51, 53 and provided with further holes 52 52 spaced from holes 50. Arm 42 has a projection 54 at its underside extending from edge 31. The major outer part of arm 42 is oifset downwardly from its end 51 so that arms 42 and 44 are coplanar.

A base plate or platform 55 is provided for the instrument 20. This plate is generally triangular in form with a ridge 56 extending from the underside of the plate at its fiat end or bottom edge 58. This ridge serves as a spacer element whose underside 60 is coplanar with the underside of arms 42 and 44. The plate 55 has a narrowed and rounded apex 62 provided with a hole 64. A threaded stud or screw 63 extends upwardly from the plate near hole 64. This screw is located on the central line of symmetry of the plate. An index line 66 provided with indicia 68 reading PLANE POSITION is located 'on the line of symmetry of the plate 55. An identification mark 70 reading ISOMETRIC may be placed near the bottom edge of the plate 55.

Two spreader arms or links 72, 74 of equal length and width are pivotally connected at one end by a screw 75 passing through holes 76, 77 in the links. The screw 75 extends through a spacer ring 78 and hole 79 in one end of short stabilizer link or arm 80. Screw 75 passes through slot 26. A thumb nut 73 is engaged on screw 75. Rivet 82 pivotally connects the other end of link 72 to arm 42 at hole 52*. Rivet 84 pivotally connects the other end of link 74 to arm 44 at hole 52*. A rivet 86 extends through holes 50 in the rounded ends of arms 42, 44; through a spacer ring 38; through hole 64 in plate 55; and through hole 32 in plate 22. A rivet 90 extends through a hole 91 in the other end of arm and through hole 28 in plate 22. Stud 63 extends through slot 30 and is engaged by a thumb nut 92.

When the several parts are assembled, the undersides of arms 42, 44 are coplanar with the underside of ridge 56. The edges of the arms 42, 44 can be used as templates for ruling lines on a flat sheet disposed under the instrument. Due to the controlled relation of spreader linkage 72, 74 by slot 26, control of arms 42, 44 by spreader links 72, 74, and manner of mounting the arms 42 and 44 to the plate 22, arms 42 and 44 will move simultaneously the same number of elliptical degrees around plate 22. Their inner edges will always be located at the same respectively numbered graduations on adjacent scales. It will be noted, particularly in FIG. 6, that graduations 24 are ruled in three repeated consecutive scales of ninety elliptical degrees each. The graduations can be doubly and reversely numbered with one set of numbers in each scale ranging from to 90 and the other set of numbers ranging from 90 to 0 in each scale, reading around the periphery of plate 22. In FIG. 1, the arms 42, 44 are each shown set at 25 left of adjacent zeros. Arm 42 could be moved through are A to the 0 position at point 38. Arm 44 will move simulta neously through are A to the next adjacent 0 position. When the arms 42, 44 are located in any desired positions along the periphery of plate 22, the thumb nut 73 may be tightened which will lock the arms in the selected positions. Arm 80 serves to stabilize the relation of spreader links 72, 74 in slot 26, but if desired it may be omitted. Or, the slotted trammel could be eliminated using only arm 80 by riveting its one end to the common junction of links 72, 74 and transposing screw and thumb to its other end through hole 28 in plate 22. This principle of locking would be less positive.

The entire plate 22 with arms 42 and 44 is pivotable on rivet 86 as a center to set any of points 38, 39, 40 at the plane position line 66. Thumb nut 92 serves to lock the plate 22 in the selected plane position indicated by the marking of the points LEFT, RIGHT and HOR.

After the thumb nuts 73 and 92 are tightened the in strument is rigid and set for use, as will now be described. The spacer elements 49*, 49 78 and 88 fill the spaces between the planes of the arms, links and plates and insure rigidity of the instrument as set.

FIG. 1 illustrates one way of using instrument 20. Suppose a cube C, shown in dotted lines, is ruled in normal isometric projection with its axes X, Y and Z disposed 120 apart. Axis Y is vertical. The isometric view assumes a line of sight 45 to the vertical faces and 35 16 to the laterals. Suppose, now, that it is required to draw a unit turned or tilted a specific number of degrees in a specific direction in a normal isometric projection. The cube here is rota-ted forwardly 25 around the bottom horizontal X axis. Any angular division of the ellipse for whatever purpose is normally a multiplestep, time consuming problem in axononrnetric drafting descriptive geometry, and requires the use of several tools, but the present invention facilitates its accomplishment accurately, quickly and simply. The bottom edge 58 of the base plate or platform 55 is placed on line L at the upper edge of a suitable horizontally placed straight edge ruler R, shown in dotted lines. Arrows A indicate that the straight edge may be moved in vertical directions parallel to axis Y to move the instrument 2t). Arrows A indicate that the instrument may be moved horizontally on the upper edge of the ruler.

To set the instrument for drawing cube C indicated in solid lines in FIG. 1, arms 42 and 44 are moved to 25 positions counterclockwise of the zeros. Thumb nut 73 is tightened. Plate 22 is rotated to set the RIGHT point 39 at line 66 and nut 92 is tightened. The RIGHT point is selected because as the view has been established, the angular changes will occur to those lines defining the right-hand face or plane. The instrument can now be 7 moved horizontally and vertically as required to draw cube C. It will be noted that axis X remains the same in length and position because this is the axis of rotation. Edges X and X can be drawn parallel to axis X. This may be done by use of a 30 angle T indicated partially in dotted lines in FIG. 1 in association with the straight edge. The new positions of the edges or axes Y, Y and Y' are drawn by use of either edge of arm 42 as a ruler. The new positions of edges Z, Z, Z are drawn by use of either edge of arm 44. By use of suitable templates (not shown) ellipses E, E and E" can be drawn in the several faces of the rotated cube C. These ellipses represent the projections of circles on the three faces of the rotated cube.

The 3516 isometric ellipse E is inscribable in the normal position, drawn tangent to Y and Z and determining the altered dimension of the cube in its now trimetric relation. Should this relation or view of the cube be selected as a trimetric basic, one axis Y, X or Z would be positioned as the vertical. Relative scales would be required in the ratios of the three dimensions. Protractor instruments required for possible angular deviations from this basic would be the 3516 or isometric ellipse protractor for the plane of ellipse E, a 15 ellipse protractor for the ellipse of plane E and a 50 ellipse protractor for the ellipse of plane E. Had the problem been a compound deviation from the normal isometric, any additional tilt or turn could be quickly established by 15 or 50 instruments as the tilt or turn may require.

If cube C were to be rotated on axis Z then the plate 22 would be rotated to the LEFT point 38. If the cube were to be rotated on the vertical axis Y, then the plate 22 would be rotated to the HOR. point 46 This would be indication of rotation of the cube in a horizontal plane.

I It is possible to draw axes X and Z of cube C by rotating plate 22 to HOR. and by setting the arms 42, 44 to 0 positions. The vertical axis Y may be drawn by the use of any right angle set up perpendicular to line L; or it is possible to draw the normal cube position by adjusting plate 22 for each of the right and left positions in turn. For normal isometric position, it is practical to use a '306090 triangle set up on ruler R. For drawing all modified isometric projections rotated on any one axis of the normal isometric projection, and for the many other problems where angular divisions of the ellipse are required, the new instrument described would be used.

FIG. 7 illustrates a protractor plate 22 which may be used in place of plate 22 in the instrument 20. This plate is elliptical and has a longer periphery than plate 22. The graduations 24 along the periphery of plate 22 are divided into proper elliptical degrees and are correspondingly numbered. Other parts of the plate 22 corresponding to those of plate 22 are identically numbered. Plate 22 is longer on its major axis than plate 22 so that the arms 42, 44 would have slightly less available working length than when plate22 is used. Plate 22 provides the advantage of less crowding and greater spacing of the scale numbers for easier readability.

FIG. 8 shows another protractor plate 22 which may be used in place of plate 22. It emphasizes 0 and 45 positions to assist in quicker adjustments.

In FIGS. 911, plate 22 in protractor 20* is somewhat similar to plate 22 with straight sides S. The plate is cut off at edge just below slot 26 The control members are inverted. Thumb nut 73 in FIG. 10 engages screw 75* inserted through slot 26 and engaging the ends of links 1%, 102. These links are pivotally attached by rivets I04, 166 to extended fingers 42 44 of arms 42 and 44. A stabilizing link 1% is pivotally attached between screw '75 and rivet 110. Rivet extends through hole 111 at the geometrical center of slot 26 Rivet 112, which pivotally connects the lower ends of arms 42', 44, is engaged in hole 114 in plate 22. This hole is located between the ends of slot 26.

The periphery of plate 22 is marked with graduations 24 numbered in elliptical degrees. Dotted arrows in FIG. 9 show a range of movement of the arms.

FIG. 11 shows how the instrument 20 employing plate 22? without an attached platform .can be used in drawing rotated cube C. Cubes C and C are numbered and lettered identically with those shown in FIG. 1. Instead of a platform, there is provided triangle T whose bottom edge H is movable along straight edge L of ruler R. The instrument is placed with the straight bottom edge 105 on the inclined side D of triangle T. This inclined side is parallel to the axis of rotation of cube C. The triangle would be turned over for rotation on the Z axis. Rotation horizontally would require the instrument be used against edge H in vertical position. It will be noted that the arms 42 and 44' assume the required positions for use as straight edges, templates or rules in drawing the altered angles of the cube.

Wlnle the structure of instrument is simpler than that of instrument 20, the lack of attached platform 55 requires manipulation of a separate triangle; or if a drafting machine is used, its adjustment and readjustment to the proper angle is required.

In FIG. 12 is shown still another instrument 26 having certain parts which .correspond to those of instrument 2t and which are identically numbered. This instrument as illustrated is useful for the 20 dimetric system where the 20 ellipse relates to the horizontal plane. Two arcuate slots 12% and 122 are provided. The thumb nut 73 can be located at any point of either slot and locked there. The arms 42' and 44' will move simultaneously in like direction as indicated by the dotted line arrows, to retain 90 relation for the 20 ellipse.

FIG. 13 illustrates certain principles on which the control factors for any degree of ellipse are based. Illustrated is one quarter section of an isometric ellipse (l6') designated 129, and shown on a larger scale than in FIGS. 1 and 2. Line 122 extending from point 126 to point 124 establishes a dimension which in FIG. 2 is the center to center measure between rivets 86 and 84 on arm 44 and between rivets 86 and 32 on arm 42, which centers are placed on a line identical to the inside edge of each arm. Line 128 from point 86' to point 124 establishes a dimension which in FIG. 2 is the center to center measure between rivet 82 and screw 75 on link arm 72 and between rivet 84 and screw 75 on link arm 74. Point 98' is obtained by drawing an arc the radius of which is equal to the length of line 128 (from point 36 to point 124) and the center of which arc is at point 126. The are intersects line 128 at point 90. The length of line 128 from point 86 to point 90 is the center to center distance between rivets 86 and 90 in FIG. 1. Arc 26' is formed by using a radius equal to the distance from point 86' to point 124 and by centering the are on point 90'. The are is drawn from point 126 to point 130. This arc is the equivalent of the center line of trammel arc 26 in FIG. 1. This center line is the path of travel of screw 75 located at the common junction of spreader links 72, 74 and confined in slot 26.

The invention as applied to the various ellipses makes it possible to execute simple and compound angular deviaitons occurring in the vairous axonometric systems with a minimum of time and effort and with more posi tive accuracy.

'le 1 have illustrated and described the preferred embodiments of my invention, it is to be understood that I do not limit myself to the precise constructions herein disclosed and that various changes and modifications may be made within the scope of the invention as defined in the appended claims.

Having thus described my invention, what I claim as new, and desire to secure by United States Letters Patent 1. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, and a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable in like direc tion at dissimilar ratios past graduations on the plate.

2. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable in like directions at dissimilar ratios past graduations on the plate, and means for locking said pivot joint in any selected position along the slot, whereby the arms will be located at identically numbered graduations on adjacent ones of the scales.

3. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable in like direction past graduations on the plate, and a stabilizer link pivotally connected at one end to the plate at the geometrical center of said slot and connected at its other end to the spreader links at their joined ends.

4. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable past equal numbers of graduations on the plate, means for locking said pivot joint in any selected position along the slot, whereby the arms will be located at identically numbered graduations on different ones of the scales, and a stabilizer link pivotally connected at one end to the plate at the geometrical center of said slot and connected at its other end to the spreader links at their joined ends.

5. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, and a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable past equal numbers of graduations on the plate, said plate being generally elliptical in form.

6. An elliptical protractor for use in drawing rotated isometric projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, and a pair of spreader links of equal length pivotally joined together at one end thereof and pivotal- 1y attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable past graduations on the plate, the periphery of said plate having a series of straight portions each extending fortyfive elliptical degrees.

7.'An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable past graduations on the plate, the periphery of said plate having a series of straight portions each extending forty-five elliptical degrees, said periphery having another straight portion located oppositely from said slot to serve as a reference edge. i

8. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable past equal numbers of graduations on the plate, said periphery having three spaced points indicating rotational axes of isometric projections, and a platform plate pivotally attached to the protractor plate, said platform plate having an index line, said protractor plate being rotatable to set any one of said points at the index line.

9. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable past equal numbers of graduations on the plate, said periphery having three spaced points indicating rotational axes of isometric projections, a platform plate pivotally attached to the protractor plate, said platform plate having an index line, said protractor plate being rotatable to set any one of said points at the index line, and means for locking the platform and protractor plates together in any of the selected settings of said points,

10. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable past equal numbers of graduations on the plate, said periphery having three spaced points indicating rotational axes of isometric projections, a platform plate pivotally attached to the protractor plate, said platform plate having an index line, said protractor plate being rotatable to set any one of said points at the index line, said protractor plate having another circularly curved slot therein, a stud carried by the platform plate extending through 8 said other slot, and means for locking said stud to fix the protractor plate to the platform plate in any of the selected settings of said points at said index line.

11. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable past equal numbers of graduations on the plate, said periphery having three spaced points indicating rotational axes of isometric projections, a platform plate pivotally attached to the protractor plate, said platform plate having an index line, said protractor plate being rotatable to set any one of said points at the index line, means for locking said pivot joint in any selected position along the first-named slot whereby the arms will be located at identically numbered graduations on diflferent ones of said scales, said protractor plate having anohe'r circularly curved slot therein, a stud carried by the platform plate extending thorugh said other slot, and means for locking said stud to fix the protractor plate to the platform plate in any of the selected settings of said points at said index line.

12. An elliptical protractor for use in drawing rotated projections, comprising a protractor plate having its periphery divided into three scales of graduations spaced equal elliptical degrees apart, said plate having a circular slot formed therein, a pair of arms pivotally secured together near their ends and engaged pivotally with the plate, a pair of spreader links of equal length pivotally joined together at one end thereof and pivotally attached at their other ends to the respective arms, the pivot joint of the links extending through said slot and slidable along the slot so that the arms are movable past equal numbers of graduations on the plate, said periphery having three spaced points indicating rotational axis of isometric projections, a platform plate pivotally attached to the protractor plate, said platform plate having an index line, said protractor plate being rotatable to set any one of said points at the index line, means for locking said pivot joint in any selected position along the first-named slot whereby the arms will be located at identically numbered graduations on different ones of said scales, said protractor plate having another circularly curved slot therein, a stud carried by the platform plate extending through said other slot, and means for locking said stud to fix the protractor plate to the platform plate in any of the selected settings of said points at said index line, said pivot joint and said stud both being threaded, both of the locking means being thumb nuts adapted to bear on the protractor plate when tightened on the pivot joint and stud respectively.

'13. An elliptical protractor for use in drawing angular deviations from the normal occurring in axonometric projections, comprising a protractor plate having its periphery divided into scales of ninety elliptical degrees each, each scale being divided into a plurality of numbered graduations, said plate having a circular trammel means, a pair of arms pivotally secured together and engaged pivotally with the plate at the geometrical center of the protractor scales, a pair of spreader links of equal predetermined length pivotally joined together at one end thereof and pivotally attached at their other ends in predetermined relations to the respective arms, the common pivot joint of the links centering at said trammel means and sliding therealong so that the arms are movable simultaneously past graduations of adjacent scales on the plate, said periphery having spaced points indicating working positions for respective planes of an axo- 9 nornetric projection, a platform plate pivotally attached to the protractor plate, said platform plate having an index line, said protractor plate being rotatable to set any one of said points at the index line, means for locking said common pivot joint of the links in any selected position along the trammel means, whereby the arms will be located at identically numbered graduations on adjacent ones of the scales, and locking means carried by the platform plate for locking the protractor plate to the platform plate in any of the selected settings of said points at said index line, said common pivot joint of the links and said locking means stabilizing the pivot joint in certain relation on the protractor plate.

References Cited in the file of this patent UNITED STATES PATENTS 1,660,578 Reppell Feb. 28, 1928 

1. AN ELIPTICAL PROTRACTOR FOR USE IN DRAWING ROTATED PROJECTIONS, COMPRISING A PROTRACTOR PLATE HAVING ITS PERIPHERY DIVIDED INTO THREE SCALES OF GRADUATIONS SPACED EQUAL ELIPTICAL DEGREES APART, SAID PLATE HAVING A CIRCULAR SLOT FORMED THEREIN, A PAIR OF ARMS PIVOTALLY SECURED TOGETHER NEAR THEIR ENDS AND ENGAGED PIVOTALLY WITH THE PLATE, AND A PAIR OF SPREADER LINKS OF EQUAL LENGTH PIVOTALLY JOINED TOGETHER AT ONE END THEREOF AND PIVOTALLY ATTACHED AT THEIR OTHER ENDS TO THE RESPECTIVE ARMS, THE PIVOT JOINT OF THE LINKS EXTENDING THROUGH SAID SLOT AND SLIDABLE ALONG THE SLOT SO THAT THE ARMS ARE MOVABLE IN LIKE DIRECTION AT DISSIMILAR RATIOS PAST GRADUATIONS ON THE PLATE. 